The aim of the studies is to define the nature and the physiological importance of neuronal-glial interactions in the developmental control of luteinizing hormone releasing hormone (LHRH) neuronal function. The first hypothesis is that gene expression of transforming growth factor alpha (TGFalpha), a member of the epidermal growth factor (EGF) family in hypothalamic astrocytes (HA) is upregulated by some of transmitters known to stimulate LHRH secretion at puberty. The effects of excitatory amino acid (EAA) and adrenergic activation on glial TGFalpha production are proposed to be examined. In vitro HA will be treated with appropriate agonists and antagonists of metabotropic receptors for EAA or with alpha2-receptor agonist. The medium levels of prostaglandin E2 (PGE2) and TGFalpha will be measured by radioimmunoassay (RIA) and TGFalpha mRNA will be determined by quantitative reverse transcription polymerase chain reaction (RT-PCR). To define the role of glial metabotropic and alpha2-adrenoreceptor activation in the control of LHRH secretion in vivo, intracerebral implantation of test substances will be used and plasma luteinizing hormone levels will be measured by RIA. The second hypothesis is that other members of the EGF family (schwannoma-derived growth factor (SDGF) and neu differentiatic factor, recognized by neu/HER-2 receptor) interact with TGFalpha in the control of LHRH neuronal function. Time course and dose response studies on the effect of TGFalpha on SDGF gene expression in HA are planned. The technique of RT-PCR to estimate SDGF mRNA will be utilized. It is important to test that neurotransmitters affect the glial expression of SDGF by mediation of TGFalpha. The experimental protocols which will be used are similar to those described earlier. In vitro exposure of HA to SDGF and measurement of PGE2 release to the medium will allow to investigate the possibility that SDGF is able to stimulate LHRH release via PGE2 formation. The ability of TGFalpha and SDGF to activate the neu/HER2-receptor by binding to their special EGF receptors will be determined by treating HA with the growth factors. The neu/HER-2 protein will be detected by SDS-PAGE autoradiography. The next experiments will be carried out as described for TGFalpha to examine if activation of glial new/HER-2 receptors results in the release of PGE2 able to stimulate LHRH release. Successful execution of the proposed plan will provide new insights into the molecular and cellular mechanisms underlying the glial control of LHRH neuronal function.